The present invention relates to vertical type heat-treating apparatus.
In general, in heat-treating apparatus which are used in film formation processes or heat dispersion processes in the manufacturing processes of semiconductor devices, vertical type heat-treating apparatus, are widely used to reduce contamination and to save the space required.
Such vertical type heat-treating apparatus are provided with a reaction tube which is formed in a cylindrical shape, and a heat-treating furnace comprising heaters and thermal insulation material which surround the heat-treating furnace and which are provided vertically inside a housing which is substantially rectangular in shape. Furthermore, the lower portion of the heat-treating furnace provided inside the housing is provided with a standby space in which wafer boards which carry many semiconductor wafers, for example, and which are the object of processing are kept prior to processing. These wafer boards are carried into and out of the heat-treating furnace by raising and lowering means such as a board elevator or the like which moves up and down, and enables processing to be carried out by a processing gas. Then, an air exhaust mechanism is provided to the heat-treating apparatus so that the high temperature unit and the processing gas which remain inside the heat-treating furnace and which are discharged from the heat-treating furnace, can be discharged to outside of the furnace.
Because there is such a mechanism, vertical types of heat-treating apparatus have far less installation space when compared to the horizontal type thereof. Furthermore, it is possible to load and unload the wafer boards to inside the heat-treating furnace without direct contact with the reaction tubes. Because of this, it is possible to have less contamination for the entire apparatus.
Also, with the vertical type of heat-treating apparatus, even less contamination is promoted by a cleaning gas being taken in through a dust removal filter and then into the standby space so that the adhesion of contaminating particles to the semiconductor wafers in the standby space is prevented. Furthermore, the cleaning gas that passes through this standby space is exhausted to a clean room which is provided for the maintenance of the heat-treating apparatus, and to a separate maintenance room.
However, with todays increased requirements for mass production, higher levels of integration and increasing levels of fineness for semiconductor devices, the degree of cleanliness of clean rooms is required to be of class 10 or more (i.e. 10/ft.sup.3 for particles of 0.2 .mu.m). However, with a conventional heat-treating apparatus as described above, a configuration where a cleaning gas which has been taken in once is discharged to the maintenance room, it is difficult to maintain the degree of cleanliness of the maintenance room at, for example, even class 100/ft.sup.3. Because of this, the particles which are discharged from the heat-treating apparatus leak through the apparatus from the side of the maintenance room to the side of the clean room and adhere to the semiconductor wafers being processed to, therefore, cause the problem of a reduced yield. In particular, the ultrafineness accuracy of semiconductor wafers continues to become smaller and currently there is the transition from a minimum dimension of 1.0 .mu.m to 0.5 .mu.m and so it is strongly desirable that the industry solve this problem.
Not only this, when there is the heat-treatment of semiconductor devices, various types of toxic gases such as phosphine (PH.sub.3), arsenic (As) and the like are used as the processing gases. Conventionally, the amounts of these processing gases used, have been relatively small and only a small amount of toxic gas remains inside the heat-treating apparatus, thereby making it possible to perform sufficient exhausting of the air by using an exhaust mechanism provided at the entrance to the heat-treating apparatus. Because of this, it was possible to maintain the required degree of cleanliness even if the cleaning gas that passes through the standby space formed inside the heat-treating apparatus was exhausted in the same state to the maintenance room.
However, the sizes of semiconductor wafers themselves are becoming larger and there is the tendency to change from sizes such as five or six inches, for example, to eight inches and there is also the tendency for the amounts of the processing gases used to increase. Because of this, it is not possible to perform sufficient exhausting with an exhaust mechanism as has been conventionally provided to the entrance of the heat-treating apparatus, and there is the same problem of the level of safety that the toxic gases propose to the operators who operate the apparatus inside the clean room.
In particular, the injection operation of impurities such as P or As or the like that are introduced when doping is performed to the semiconductor wafers has been conventionally performed by ion injection apparatus or the like. However, with these apparatus, there are various types of problems concerning the difficulty of making the semiconductors finer and which are due to the thermal efficiency and the thermal dispersion which accompanies annealing after the injection of ions. Because of this, recent technological development has meant that ion introduction processes such as these tend to be carried out at the same time as the film formation processes in vertical heat-treating apparatus, and this means that it is also desirable that this problem be eliminated.